Molybdenum-tantalum alloys



Patented May 11, 1954 UNITED STATES PATENT OFFICE MOLYBDENUM-TANTALUM ALLOYS No Drawing. Application October 6, 1951, Serial No. 250,205

13 Claims.

This invention relates to alloys of molybdenum and tantalum and more specifically to large, sound cast molybdenum-tantalum alloy ingots which are capable of being worked at elevated temperatures by forgin pressing, rolling, extrusion and other similar methods. This invention is also concerned with molybdenum-tantalum alloys containing minor quantities of other elements and to such alloys in which a part of the molybdenum has been replaced by tungsten. Such alloys are useful in applications which require metals of high strength or hardness at both room and elevated temperatures, and more specifically in such applications as piercing points for forming seamless steel tubing, electrodes for heating molten glass, die-casting dies for brass and other metals, etc. This application is a continuationin-part of applicants copending application, Serial No. 218,524, filed March 30, 1951, now abandoned.

The principal object of this invention is to provide improved cast molybdenum-base alloys which are capable of being worked at elevated temperatures.

A further object of this invention is to provide cast molybdenum-base alloys which can be worked at elevated temperatures and exhibit a tendency to retain work-hardening at elevated temperatures.

Another object of this invention is to provide improved cast molybdenum-base alloys which possess increased hardness at both room and elevated temperatures above that which is possessed by pure molybdenum.

The terms cast and casting as used in this specification are intended to designate the product resulting from the melting of metal and solidifying the same in a mold whether or not the metal has been subjected to subsequent working or machining. The term "casting is also used to designate any process or method which involves melting metal and solidifying the same in a mold.

In accordance with this invention, cast molybdenum alloys having the above properties are produced when tantalum is employed as an alloying element. Cast alloys of molybdenum and tantalum are capable of being worked at elevated temperatures only if they contain limited amounts of tantalum and other elements.

It has previously been established that the presence of minute amounts of oxygen in a casting of molybdenum or a molybdenum-base alloy seriously impairs or destroys the capacity of the casting to be Worked at elevated temperatures if the oxygen is segregated at the grain boundaries in the form of certain metallic oxides. The detrimental oxide is visible on microscopic examination of intergranular fractures and is believed to consist largely of M002. However, the oxides of certain other metals, if present, are also detrimental. In any event, when examined microscopically, castings Which can be worked at elevated temperatures have no visible oxide segregations at the grain boundaries which are similar to the manifestations of M002. Cast molybdenum containing less than about .00l% oxygen can be worked at elevated temperatures but it is very difficult in the production of cast ingots of molybdenum and its alloys to reduce the oxygen content of the metal to such a low value.

As set forth in the patent to Frederick P. Bens et al., No. 2,580,273, the detrimental oxide segregation is not found in molybdenum castings containing not more than .005% oxygen if small amounts of carbon are present. Such castings can be Worked at elevated temperatures.

It is now found that the detrimental oxides may also be eliminated by incorporating in the casting certain metals which have a stronger affinity for oxygen than does molybdenum and form oxides which either do not segregate at the grain boundaries or, if segregated at the boundaries, provide greater intergranular cohesion than does the oxide of molybdenum. Aluminum and beryllium have been found to fulfill these requirements, and forgeable castings of molybdenum and molybdenum-base alloys containing up to a maximum of .05.% oxygen have been produced by incorporating small quantities of aluminum or beryllium or both in the casting. Carbon may also be present, if desired, and small quantities of carbon or aluminum are particularly beneficial in molybdenum-base alloys containing beryllium. 1

The effect of oxygen on the molybdenum-tantalum alloy castings of the present invention is similar to its effect in other molybdenum-base alloy castings, and consequently it is necessary to eliminate segregations of molybdenum oxide at the grain boundaries if the casting is to be worked at elevated temperatures. This is preferably done by incorporating carbon, aluminum or beryllium in the alloy, either singly or in combination. This critical effect of oxygen on the capacity of the alloy to be Worked at elevated temperatures is peculiar to cast alloys as distinguished from those produced by sintering metal powders.

If carbon is present in amounts between .01% and 04% and no aluminum or beryllium is pres-'- out, the maximum oxygen content which can be tolerated in a casting that must be worked at elevated temperatures is about 005%. The minimum quantity of residual carbon should, preferably, increase within these limits as the residual oxygen content approaches 005%. Larger amounts of carbon up to a maximum of about .25 may be present in a casting that must be worked at elevated temperatures, but the resulting additional carbides increase the difficulty of hot-working the cast alloy without imparting other advantages and, therefore, it is'pref'erred' that the carbon not exceed'about 07%.

If aluminum or beryllium is present in adequate quantities, the maximum oxygen content which can be tolerated in a casting that-mustbe worked at elevated temperatures is about 05%. The quantity of aluminum or beryllium must be at least sufficient to stoichiometrically react with the oxygen present in the final alloy to form A1203 or BeO, and is preferably three times that quantity in thecase of aluminum. Thus, aluminum in the range of 003% to .4% or beryllium in the range of 001% to 03% may be present. In actual practice, aluminum is preferred to beryllium for this purpose and, if beryllium is used, it is preferred to use small quantities of aluminum or carbon with the beryllium. When aluminum is present within the ranges stated, residual carbon is preferably omitted altogether or does not exceed 02%. However, cast molybdenum-tantalum alloys containing aluminum and as high as 06% carbon can be worked at elevated temperatures. When beryllium is used, it is preferred that the carbon not exceed 06%.

Excellent results are achieved in the working oi" molybdenum-tantalum castings containing carbon in the range of 02% to 05% and oxygen less than 003%; or aluminum from 003% to 2% and oxygen less than 02%; or beryllium from .001 to.02% and oxygen less than 02%. Quantities of aluminum and beryllium above the minimum required to react with the oxygen have other beneficial effects and hence aluminum may be present upto a maximum of about 2.5% of beryllium up to a maximum of about However, as set forth hereinafter, the amount of tantalum present must be reduced below its maximum of the aluminum exceeds about .4% or the beryllium exceeds about 03% and the alloy is to be worked at elevated temperatures.

Molybdenum-base alloys containing aluminum or beryllium and the herein-disclosed process of producing such alloys are more fully disclosed and claimed in applicants copending applications, Serial No. 250,202, on Molybdenum-Tungsten-Ahuninum Alloys, and Serial No. 250,201, on" Cast Alloys and Method for HeatTreating the Same, both filed concurrently herewith.

When molybdenum is alloyed with tantalum, the tantalum addition increases the hardness and strength both at room and elevated temperatures. Molybdenum-tantalum alloy castings also exhibit anunexpected tendency to retain at elevated temperatures, hardening induced by working; Cast molybdenum-tantalum alloys containing 5% to 9% tantalum can be worked at elevated temperatures to a beneficial degree but it is apparently impossible to hot-work cast molybdenum-base alloys containing more than about 9% tantalum. The difiiculty of working increases with increasing tantalum and oxygen contents. Greater ease in working the alloy is secured when the oxygen content is proportionately decreased toward the practical minimum ofabout 001% as the tantalum content increases toward 9%. The addition of 5% tantalum has been found to be effective in improving the high temperature properties of the alloy, but percentages of tantalum below about 5% "were not found to be particularly advantageous. Ehe preferred range of tantalum content is 1% to 7.5%. Alloys of from 5% to 9% tantalum in molybdenum comprise solid solutions at room temperature.

If desired, tungsten may be present in an amount not exceeding the molybdenum present without destroying forgeability or" the alloy. The addition of tungsten has a tendency to increase the hardness the alloy, and it has been found impossible to wori: cast alloys containing the maximum percentages of both tungsten and tantalum. Cast alloys which can be worked at elevated temperatures will result, however, if, as the'tungsten percentage is increased toward its maximum of about 50 the tantalum percentage is proportionately decreased toward the minimum of 5%. It is likewise desirable for the oxygen content to be proportionately decreased toward the practical minimum of about 001% as the tungsten content is increased. It is to be understood that the relationship between he tungsten and tantalum percentages relates only to the maximum percentage of tantalum which may be present for given percentage of tungsten without interfering with working, and that alloys containing less tantalum and tungsten than the maximums fall within the scope of this invention. Actually, it is preferred to use no tungsten or amounts less than l0%.

Minor quantities of other elements may also be present. Thus, certain hereinafter listed transition elements produce advantageous effects when added to the molybdenum-tantalum alloys of the present invention. However, to produce a cast alloy which can be worked at elevated temperatures to a beneficial degree, the amounts of tungsten, other transition elements, aluminum and beryllium must be limited; the preferred alloys contain at least molybdenum. even in pure binary alloys of molybdenum, the following beneficial. transition elements should not be present in amounts exceeding the following percentages if the alloy is to be worked at elevated temperatures:

Per cent Titanium l. 4 .0 l 'anadium 7 .0 Zirconium 2 .0 Chromium 2 .0 Iron 1 Cobalt .9 Nickel .4 Columbium 10.0

num, will produce a hardness at 1000 F. of 200 'V. P. N. (Viokers pyramid numeral) in, an annealed casting. It has not been possible with normal working-techniques to achieve a worthwhile percentage of recovery from the working of metals and alloys having greater hardness, but a beneficial hot-working at temperatures substantially above 1600 F. may be performed on the alloys of the present invention, provided the hardness at 1600 F. does not exceed about 200 V. P. N. in an annealed casting. The effects of all of the above-mentioned metals, also tantalum and tungsten, on hot-hardness are additive and, therefore, when two are present the maximum permissible amount of one should be proportionately reduced from its maximum given to the extent that the other approaches its maximum if the alloy is to be capable of being Worked at elevated temperatures to a beneficial degree. Still further reductions on the same basis must be made if more than two are present, and in all cases less than those maximums gives the best results. From the standpoint of high strength and hardness at elevated temperatures in the molybdenum-tantalum alloy casting that is well adapted to working at elevated temperatures, the preferred alloying transition elements are titanium, vanadium, columbium and zirconium.

Molybdenum-base alloys characterized primarily by the beneficial effects of zirconium, columbium, vanadium and titanium, respectively, are more fully disclosed and claimed in applicants copending applications, filed concurrently herewith, as follows: Serial No. 250,206, Molybdenum-Zirconium Alloys; Serial No. 250,207, Molybdenum-Columbium Alloys; Serial No. 250,203, Molybdenum-Vanadium Alloys; Serial No. 250,204, Molybdenum-Titanium Alloys.

It has been noted that additions of 01% to 5% thorium to cast molybdenum or tungsten increase the temperature at which the worked metals may be heated without excessive grain coarsening and without becoming embrittled. Thus, thorium within the range stated may be present in the alloys of this invention.

Therefore, the expression balance consisting essentially of molybdenum occurring in the following claims means that the alloys called for are those whose primary characteristics result from the presence of tantalum in molybdenum, but that the alloys may also contain quantities of unspecified elements, such as the above-mentioned transition elements, which do'not appreciably impair the beneficial effects of tantalum or destroy the capacity of the alloy to be worked at elevated temperatures to a beneficial degree.

By way of example, the following alloys may be cast, hot-worked successfully, and are useful;

Example 1 Tantalum 8.46%.

Carbon 045%.

Oxygen Less than 005%.

Molybdenum Balance.

Example 2 Tantalum 2.5%.

Carbon 045%.

Oxygen Less than 005%.

Molybdenum Balance.

Eazample 3 Tantalum- 4.5%.

Carbon 045%.

Oxygen Less than 005%.

Molybdenum Balance.

Example 4 Tantalum." 4%. Tungsten 5%. Carbon .02%. Oxygen Less than .0025%. Molybdenum Balance.

Example 5 Tantalum 5%. Aluminum 15%. Oxygen .02 Molybdenum Balance.

" Example 6 Tantalum 3%. Carbon .01 Beryllium .02%. Oxygen .03%. Molybdenum Balance.

The alloys of this invention may be made by a variety of procedures, but cast alloys containing carbon are preferably made by the process which consists in the steps of (l) mixing molybdenum, tantalum, carbon and any other desired elements in the form of powders, in the desired proportions; (2) pressing the mixture into successive pellets to form a continuous rod; (3) sintering the rod to impart sufficient strength to the same to render it self-supporting; and (4) arcmelting the sintered rod as a consumable 8180-. trode in a vacuum and. collecting the metal directly into a water-cooled copper mold.

The starting materials used in the process are commercially pure molybdenum powder, preferably containing not more than about 05% oxygen, and. commercially available tantalum and carbon powders as well as powders of any other elements employed. Metals in the form of small chips or granules may comprise part of the charge. The starting materials are analyzed for carbon and oxygen and, the amount of carbon required to stoichiometrically react with the oxy-- gen present to form carbon monoxide and to provide a residual carbon content of at least 0.1% but less than 25% is employed.

The powder charge is fed into an extrusion die positioned beneath the ram of a reciprocating press wherein successive pellets of the powder material are pressed continuously on top of preceding pellets to form a continuous rod of pressed metal powders. Pelleting pressures of approximately 10,000 to 20,000 p. s. i. have been used, with 14,000 p. s. i. normally being adequate. The pressing is accomplished in a vacuum-tight container.

Sufdcient strength to make the pressed metal rod self-supporting is imparted by sintering the rod in vacuum at a temperature of approximately 2400" F. to 2900" F. for approximately a, quarter of a minute to several minutes. Sintering may be accomplished by any well-known method of heating; electrical resistance heating is preferred.

The sintered rod is then used as a consumable electrode in a vacuum arc furnace. Melting is started by striking an arc between the rod and a 7 starting electrode comprising a pile of chips of the same or similar alloy placed on a disc of molybdenum at the bottom of the casting mold. A water-cooled copper mold has been found suitable for receiving the molten molybdenum alloy without contaminating the alloy with copper. Molten alloy striking the water-cooled copper mold quickly solidifies, forming a protective coating on the surface of the mold. Thereafter, the

liquid alloy becomes the lower electrode andthe upper, consumable electrode is mechanically fed toward the lower, liquid electrode to maintain continuous melting with the proper arc spacing.

Steps 2, 3 and rare carried out at as low a pres-. sure as possible. The pressure should not exceed a. maximum of 500 microns and is preferably below 100 microns. All three of these steps may be carried out in the same closed container.

If aluminum or beryllium or any other relatively volatile element is employed in the alloy, the above-described process cannot be practiced under the degree oi vacuum set forth above and hence it; is necessary to employ an inert atmosphere of higher pressure in the melting chamber. An argon or helium atmosphere at or slightly above atmosphericpressurehas been found suitable ior thispurpose. Except for the. change from. vacuum to an inert atmosphere at higher pressure, they process previously described may be used. The desired quantities of aluminum or beryllium are added to the mixture of metal powders which are sintered to produce the consumable electrode.

Inasmuch as extremely minute quantities of oxygen impair the capacity of the alloy casting to be worked at elevated temperatures, the starting material should be as low in oxygen as possible and it is necessary to avoid the introduction of significant quantities of oxygen as a contaminant in the inert atmosphere. The inert atmosphere may be purified by circulating it through a commercial drying tower before introduction intothe casting container. The gas may be recirculated or re-used after passing over a bed of titanium metal maintained at approximately 1500 F., and a bed of magnesium metal maintained at approximately 1100 F. Because of the relatively high volatility of aluminum and beryllium at the arc temperature, pressure of the inert atmosphere within the casting container is preferably maintained at substantially atmospheric pressure or slightly above, for example, up to about 15.5 pounds per square inch. The casting container is first evacuated and then flushed with the inert gas; and, during operation, the gas is bled into the casting container to maintain atmospheric pressure or slightly above.

If carbon is employed, in addition to aluminum or beryllium, the partial pressure of carbon monoxide in the melting chamber should be maintained below about 100 microns. In some cases, this may require a flow of purified inert gas through the chamber. I One suitable form of the apparatus for use in forming, sintering and melting the powder rod is disclosed in the copending application of Edgar K. Leavenworth, Serial No. 787,797, filed November- 24, 1947, now Patent No. 2,651,952.

Results from a large number of tests of molybdenum-tantalum alloys indicated that these alloys possess an unexpected tendency to retain work-hardening at elevated temperatures. The testing procedure and typical results are set forth below. The alloy of Example 1 in the form of a bar 1 inches in diameter and 2 inches long having a hardness of 232 V. P. N. in the annealed casting was heated in the range of 2500 F. to 2600 F. and extruded in a die having a diameter of .78' inch. After extrusion, the hardness was 317 V. P. N. The as-extruded bar was then annealed for one hour at 2200 F. without any loss in hardness. A duplicate bar, after annealing. forl hour at- 2400" F., reduced in hardness onlyrto. 284 V; P. N. The superiority of molybdenum-tantalum alloys over molybdenum in relit taining work-hardness at elevated temperatures is apparent when it is-noted that, in the absence of tantalum, molybdenum containing the same carbon content and similarly treated lost all of its work-hardness after 1 hour at 2000 F.

All of the proportions given herein are proportions by weight in the final alloy, and such proportions are proportions of the total alloy unless otherwise stated.

What is claimed is:

1. A cast alloy consisting of at least 85% molybdenum and characterized by its capacity to be worked at elevated temperatures and its capacity to retain a significant amount of Work hardness after one hour at 2200" F., said alloy containing from .50% to 9% tantalum, from 003% to .4% aluminum, from zero to .02% carbon, oxygen less than 02%, and the balance consisting essentially of molybdenum.

2. A cast alloy consisting of at least 85% molybdenum and characterized by its capacity to be worked at elevated temperatures and its capac ity to retain a significant amount of Work hardness after one hour at 2200 F., said alloy con taining from .50% to 9% tantalum; at least one element from the group consisting of carbon from .01% to .25%, aluminum from 003% to 2.5% and beryllium from 001% to 25%; metal from the group consisting of the transition elements titanium from zero to 14%, vanadium from zero to 7%, chromium from zero to 2%, iron from zero to- 1.3%, cobalt from zero to 9%. nickel from zero to .4%, zirconium from zero to 2%, columbium from zero to 10%, and tungsten from zero to 10%, the total amount of metal from said group of transition elements being further limited to an amount within the range from none to the amount which will increase the hardness of the annealed casting to a value not exceeding 200 V. P. N. at 1600 F.; and the balance consisting essentially of molybdenum.

3. A cast alloy consisting of at least 85% molybdenum and characterized by its capacity to be worked at elevated temperatures and its capacity to retain a significant amount of work hardness after one hour at 2200" F., said alloy containing from .50% to 9% tantalum; from 003% to .4% aluminum; from zero to .02 carbon; oxygen less than 02%; metal from the group consisting of the transition elements titanium from zero to 14%, vanadium from zero to 7%, chromium from zero to 2%, iron from zero to 1.3%, cobalt from zero to .9%, nickel from zero to .4%, zirconium from zero to 2%, columbium from zero to 10%, and tungsten from zero to 10%, the total amount of metal from said group of transition elements being further limited to an amount within the range from none to the amount which. will increase the hardness of the annealed casting to a value not exceeding 200 V. P. N. at 1600 F.; and the balance consisting essentially of molybdenum.

4. A cast alloy consisting of at least 85 molybdenum and characterized by its capacity to be worked at elevated temperatures, said alloy containing from .50% to 9% tantalum; at least one element from the group consisting of carbon from .01% to 25%, aluminum from 003% to 2.5% and beryllium from 001% to 25%; metal from the group consisting of the transition elements titanium from zero to 14%, vanadium from zero to 7%, chromium from zero to 2%, iron from zero to 1.3%, cobalt-fromzero to, .9 nickelf-rom zero to 4%, zirconium from zero, to 2%. columbium fr m. .zemo; 10%., and tungstennfrom. zerQ to 10%, the-total amount of metal from said group of transition elements being further limited to an amount within the range from none to the amount which will increase the hardness of the annealed casting to a value not exceeding 200 V. P. N. at 1600 F.; and the balance consisting of molybdenum.

5. A cast alloy characterized by its capacity to be worked at elevated temperatures and its capacity to retain a significant amount of work hardness after one hour at 2200 F., said alloy casting comprising from 50% to 9% tantalum, carbon from .01% to .25 oxygen not more than 005%, and the balance consisting essentially of molybdenum.

6. A cast alloy characterized by its capacity to be worked at elevated temperatures and its capacity to retain a significant amount of work hardness after one hour at 2200 F., said alloy casting comprising from 50% to 9% tantalum, oxygen not more than aluminum in an amount at least sufficient to react with all of the oxygen present and not more than 2.5%, the maximum amount of aluminum within the range stated being reduced toward 4% as the amount of tantalum approaches its upper limit, and the balance consisting essentially of molybdenum.

7. A cast alloy characterized by its capacity to be worked at elevated temperatures and its capacity to retain a significant amount of work hardness after one hour at 2200 said alloy casting comprising from 50% to 9% tantalum, oxygen not more than 305%, beryllium in an amount at least sufiicient to react with all of the oxygen present and not more than 25%, the maximum amount of beryllium within the range stated being reduced toward .03% as the amount of tantalum approaches its upper limit, and the balance consisting essentially of molybdenum.

8. A cast alloy consisting of at least 85% molybdenum and characterized by its capacity to be worked at elevated temperatures, said alloy casting containing from 50% to 9% tantalum, carbon from .01% to 25%, oxygen not more than .005%, metal from the group consisting of the transition elements titanium from zero to 14%, vanadium from zero to 7%, chromium from zero to 2%, iron from zero to 1.3%, cobalt from zero to .9 nickel from zero to .4%, zirconium from zero to 2%, columbium from zero to 10%, and tungsten from zero to 10%, the total amount of metal from said group of transition elements being further limited to an amount within the range from none to the amount which will increase the hardness of the annealed casting to a value not exceeding 200 V. P. N. at 1600 F., and the balance consisting of molybdenum.

9. A cast alloy consisting of at least 85% molybdenum and characterized by its capacity to be worked at elevated temperatures, said alloy casting comprising from 50% to 9% tantalum, oxygen not more than .05%, aluminum in an amount at least sufiicient to react with all of the oxygen present and not more than 2.5%, the maximum amount of aluminum within the range stated being reduced toward 04% as the amount of tantalum approaches its upper limit, metal from the group consisting of the transition elements titanium from zero to 14% vanadium from zero to 7%, chromium from zero to 2%, iron from zero to 1.3%, cobalt from zero to .9%, nickel from zero to .4%, zirconium from zero to 2%, columbium from zero to 10 and tungsten o zero to 10%, the total amount of metal from said group of transition elements being further limited to an amount within the range from none to the 10 amount which will increase the hardness of the annealed casting to a value not exceeding 200 V. P. N. at 1600" F., and the balance consisting of molybdenum.

10. A cast alloy consisting of at least molybdenum and characterized by its capacity to be worked at elevated temperatures, said alloy casting comprising from .50% to 9% tantalum, oxygen not more than .05%, beryllium in an amount at least sunicient to react with all of the oxygen present and not more than 25%, the maximum amount of beryllium within the range stated being reduced toward .03% as the amount of tantalum approaches its upper limit, metal from the group consisting of the'transition elements, titanium from zero to 9%, vanadium from zero to 7 chromium from zero to 2 iron from zero to 1.3%, cobalt from zero to .9%, nickel from zero to .4 zirconium from zero to 2%, columbium from zero to 10%, and tungsten from zero to 10%, the total amount of metal from said group of transition elements being further limited to an amount Within the range from none to the amount which will increase the hardness of the annealed casting to a value not exceeding 200 V. P. N. at 1600 F., and the balance consisting of molybdenum.

11. A cast, molybdenum-base alloy characterized by its capacity to be worked at elevated temperatures, said alloy casting comprising from 50% to 9% tantalum, carbon from 01% to 07%, oxygen not more than 003%, and the balance consisting of molybdenum.

12. A cast, molybdenum-base alloy characterized by its capacity to be worked at elevated temperatures, said alloy casting comprising from .50% to 9% tantalum, aluminum from 003% to .4%, carbon not more than .06 oxygen not more than .05%, the minimum amount of aluminum within the range stated being that required to combine with all of the oxygen in the alloy to form aluminum oxide, and the balance consisting of molybdenum.

13. A cast, molybdenum-base alloy characterized by its capacity to be worked at elevated temperatures, said alloy casting comprising from 50% to 9% tantalum, beryllium from .001% to 03%, carbon not more than 06%, oxygen not more than 05%, the minimum amount of beryllium within the range stated being that required to combine with all of the oxygen in the alloy to form beryllium oxide, and the balance consisting of molybdenum.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 969,064 Kuzel Aug. 30, 1910 1,363,162 Myers et al. Dec. 21, 1920 1,385,072 Grenagle July 19, 1921 2,143,853 Armstrong Jan. 17, 1939 2,188,405 Hensel et al. June 30, 1940 2,304,297 Anton Dec. 8, 1942 OTHER REFERENCES Parke et al.: Treatise in Transactions of Amer ican Institute of Mining and Metallurgical Engineers, vol. 171, 1947, pages 416-430.

Kessler et al., 1949. Preprint No. 33 of paper presented at the American Society for Metals Convention, Cleveland, Ohio, October 17-21, 1949. 

1. A CAST ALLOY CONSISTING OF AT LEAST 85% MOLYBDENUM AND CHARACTERIZED BY ITS CAPACITY TO BE WORKED AT ELEVATED TEMPERATURES AND ITS CAPACITY TO RETAIN A SIGNIFICANT AMOUNT OF WORK HARDNESS AFTER ONE HOUR AT 2200* F., SAID ALLOY CONTAINING FROM .50% TO 9% TANTALUM, FROM .003% TO .4% ALUMINUM, FROM SERO TO .02% CARBON, OXYGEN LESS THAN .02%, AND THE BALANCE CONSISTING ESSENTIALLY OF MOLYBDENUM. 